Do not attempt to parse blank responses from cancelled XHR POST requests

An XHR POST request may be cancelled by navigating away from the page while the timeline is loading.  This causes alert spam on Chrome and Safari.
Merge pull request #1041 from nzmsv/master

Do not attempt to parse blank responses from cancelled XHR POST requests
Noting #1041.
#1037 deleted Javadoc which should rather have been corrected to follow some refactorings.
More natural to use Timer for ProgressiveRendering.
In /asynchPeople, check progressive rendering cancelation status between each user; UserAvatarResolver could be slow.
Handy way to slow down ProgressiveRendering when starting Jenkins in test mode.
Generate a unique status div ID for <l:progressiveRendering/> so we do not clash with anything else on the page.
Trying to make test pass after changing the progress bar to use a generated ID.
Also trying (without success) to diagnose an earlier local test failure.
Remove javadoc reference to non-existent class in test source code
Fully qualify JenkinsRule reference from package-info javadoc
[FIXED JENKINS-20219] Filter for installed plugins

Added filter support for installed tab of plugin manager
Merge pull request #1047 from MarkEWaite/javadoc-fixes-m

Javadoc fixes in two tests
Merge branch 'master' of github.com:iplaman/jenkins into iplaman-master
[JENKINS-20219] Noting #1048.
fixed typos in french translation
Merge pull request #1049 from hboutemy/master

fixed typos in french translation
Translation pt_BR - Jenkins Meetup Sao Paulo
Merge branch 'master' of https://github.com/jenkinsci/jenkins
[JENKINS-4543] Noting retroactively.